EFFECTS OF DISPERSION AND AGGREGATION OF SILICA IN THE REINFORCEMENT OF POLY(METHYL ACRYLATE) ELASTOMERS

Composites were prepared from methyl acrylate monomer and silica parti cles to which 3-(trimethoxysilyl)propyl methacrylate groups had been g rafted. The silica particles were bonded onto poly(methyl acrylate) th rough participation of their methacrylate groups in the polymerization of the methyl acrylate to form an elastomeric matrix. If the polymeri zation was done promptly after the ingredients were mixed, the silica particles were randomly dispersed. On the other hand, if sufficient ti me was permitted, the particles spontaneously formed regular arrays wi thin the monomer which, on polymerization, yields the elastomer. Final ly, if the particle dispersion was first dried and then blended into t he monomer prior to polymerization, an aggregated arrangement was obta ined. Although the elastomers having regularly ordered silica dispersi ons exhibited novel optical properties, they showed little difference in mechanical properties relative to those with randomly dispered sili ca. The elastomers having aggregated silica, however, had significantl y improved mechanical properties, relative to the other two types. Thi s is consistent with frequent observations in the rubber industry that halting compounding short of complete filler dispersion can give the best balance of mechanical properties.